FBI on trial for warrantless Stingray mobile spying

In an Arizona court case, the FBI has been forced to defend its use of a phony cellphone tower dubbed Stingray that it's using to analyse mobile phone traffic and identify suspects.

The Stingray system came to light in the case of Daniel David Rigmaiden, who stands accused of reaping millions of dollars from filing phony tax returns on the basis of identity theft. The FBI were able to catch Rigmaiden in 2008 by tracking down the 3G card he was using as a modem, but it didn't disclose that the Stingray had been used in this process without a warrant.

The Stingray system uses a dummy mobile base station that mimics a standard cellphone tower, and can locate cellphones by their International Mobile Station Equipment Identity numbers, and monitor calls. This works even if the phone isn't in use, since the Stingray can provoke a response from any device that's switched on.

It's a broadly sweeping tool that collects data on all mobile devices in the area for analysis, and can then be used to triangulate down to a specific device by shifting to a new position and getting a new signal lock. But the FBI has argued in court that this device needs no warrant, despite the very broad nature of the information it collects.

"The government cannot obtain judicial approval for a search using sophisticated, uniquely invasive technology that it never explained to the magistrate," reads the amicus brief on Thursday's case from the ACLU and EFF.

"To construe this Order as a valid 'warrant' authorizing the use of the stingray would prevent magistrates from making informed determinations on warrant applications and encourage the government to keep magistrates in the dark."

The FBI argues that the devices themselves are relatively new and their legal status hasn’t been fully considered. But documents obtained by the ACLU show that the device was in use for at least three years without warrants, despite judicial concerns being raised.

At issue is the Fourth Amendment, which states:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

Since the Stingray is capable of searching within someone's home and on their property, the ACLU and others argue that its use requires a warrant, particularly as its information-gathering powers are large and include innocent third-parties – particularly if that data can be used in later investigations.

If the court rules against the FBI, it will be forced to ask for a warrant when using the device. While this might slow the organization down for a day or two, such a move would do a lot to reassure those not under investigation that their calls and location remain private.

"Judicial supervison of searches is most needed when the government uses new technologies to embark into new and unknown privacy intrusions. But when the government hides what it's really doing, it removes this important check on government power," said the EFF in a statement.

"We hope the court sees its been duped, and makes clear to the government that honesty and a warrant are requirements to using a Stingray." ®